This application claims the priority benefit of Taiwan application serial no. 89123557, filed on Nov. 8, 2000.
1. Field of the Invention
The present invention relates to a structure and package of a heat spreader substrate. More specifically, the present invention relates to a cavity down package.
2. Description of the Related Art
With the rapid development in integrated circuits and continuous improvement in semiconductor devices, an important feature of a semiconductor is to have high efficiency, high integration, high speed and to be a multi-functional device. Moreover, the packaging quality of this device is becoming more demanding. For example, high density, high heat diffusion functions and high reliability are very important factors in the development of semiconductor packaging.
FIG. 1 is a schematic cross-sectional view showing a structure of a cavity down ball grid array (BGA). The structure of a cavity down BGA 20 is disclosed in U.S. Pat. No. 5,420,460 and U.S. Pat. No. 5,397,921. The carrier comprises a heat spreader 22 and a substrate 26. The heat spreader 22 is adhered on the substrate 26 by an adhesive material 28. A cavity 24 is formed on the middle of the heat spreader 22 and is used to carry a chip 40. A patterned trace layer and an insulating layer are laminated on the substrate. A mounting pad 30 and a ball pad 32 are formed on the surface of the patterned trace layer, and a solder mask 34 covers the surface of the patterned trace layer. The chip 40 comprises an active surface 40a and a backside 40b. The backside 40b of the chip 40 is adhered on the bottom of the cavity 24 by an adhesive material 36. A bonding pad 42, which is formed on the active surface 40a of the chip, is connected to the mounting pad 30 of the substrate 26 by gold wires 50. A molding compound 52 covers the chip 40, gold wires 50 and the mounting pad 30. A solder ball 54 is formed on the surface of the ball pad 32.
FIG. 2 is a schematic, cross-sectional view showing another structure of a cavity down BGA. The cavity down BGA package is disclosed in U.S. Pat. No. 6,020,637. The carrier is made of a heat spreader 102, a ground plane 104 and a flex substrate 110. The heat spreader 102, the ground plane 104 and the flex substrate 110 are stacked on each other with insulating adhesive materials 106 and 108. A cavity is formed on the middle of the ground plane 104 and the flex substrate 110 to carry a chip 120. The flex substrate 110 is a flex tape interconnect substrate. A patterned trace layer and a polyimide layer are laminated on the flex tape interconnect substrate. A mounting pad and a ball pad are formed on the surface of the patterned trace layer 112. A solder mask 114 covers the surface of the patterned trace layer 112. The chip 120 has an active surface 120a and a backside 120b. The backside 120b of the chip 120 is adhered on the bottom of the cavity by an adhesive material 124. The bonding pad 122 of the active surface 120a is connected to a ground ring 116 of the ground plane 104 and to the mounting pad of the flex substrate 110. The chip 120, the gold wires 126 and the mounting pad are encapsulated with a mounting compound 128. A solder ball 130 is formed on the surface of the ball pad 112.
According to the above, a heat spreader is the main structure of the carrier. The heat spreader is made of copper, and the copper improves the heat diffusion of the package material.
Referring to FIG. 1, the cavity 24 of the heat spreader 22 is formed by an etching process. However, the etching process has a high cost, low throughput and is time consuming. On the other hand, the structure of the heat spreader is limited to its thickness because it is difficult to reduce the thickness by utilizing the conventional method. In FIG. 2, the heat spreader is made of two metals, a heat spreader 102 and a ground plane 104. Although the cavity can be mass produced by a machining method, the structure is still limited to a certain thickness after it is stacked up. Thus, the disadvantage of the conventional method is the lack of control of the thickness of the package.
It is an object of the present invention to provide a heat spreader substrate and the package thereof to reduce the thickness of the packaging.
It is another object of the present invention to provide a machining method and a process for producing a heat spreader substrate and a package to reduce the cost.
According to the present invention, a structure of a heat spreader substrate is provided. A first heat spreader has a first upper surface, a first lower surface and an opening. A second heat spreader has a second upper surface and a second lower surface. A thickness of the second heat spreader is smaller than a thickness of the first heat spreader. The second heat spreader is fit tightly into the opening. The second lower surface of the second heat spreader and the first lower surface of the first heat spreader are coplanar. The upper surface of the second heat spreader is for locating a chip. The substrate is located on the upper surface of the first heat spreader, and the opening is exposed.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, the second heat spreader of the invention can be designed into various shapes, such as a first portion of the second heat spreader being bigger than a second portion of the second heat spreader. The molding compound is utilized to fill a space between the first heat spreader and the second heat spreader in order to increase the adhesion during the molding process. A groove and a protrusion are formed respectively on a contact portion between the first heat spreader and the second heat spreader.
The purpose of forming the groove and the protrusion is to provide a secure fit for the second heat spreader into the first heat spreader. A chip is located on the cavity surface. A plurality of loop-shaped grooves are formed on the second upper surface.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.